The male (of both African and Indian) Ringnecks will develop the "ring" upon maturity. The age varies between birds, and I don't have firsthand experience, but I've heard from 18 months to 2 years a ring will start to molt in if it's a male.
It's so tough to say how old a bird is. They just don't show signs of age as distinctly as mammals do. Sometimes we can say if the bird looks juvenile or "older" but that's about all. Hard to tell by the picture, but to me it doesn't look REAL young as in under a year. Maybe people experienced with seeing many Ringnecks could take a guess, but that's all it would be from anyone, a guess. Even if a female, it's a beautiful bird. Love the maroon beak of the Africans!